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Everyday Virtualization

In Praise of VMFS

Like many other administrators, I started my virtualization experience with VMware products. In server consolidation, one technology that caught my interest early is the VMware vStorage Virtual Machine File System (VMFS). The concept of a clustered file system was new to me with my Windows background, but it's now something we take for granted in the virtualization world. Those who work with me frequently roll their eyes whenever I get a chance to explain VMFS to someone new, as I make the obligatory comment, "VMFS is the most underrated technology that VMware has ever made."

It's underrated because technologies like traditional VMotion and Storage VMotion are enabled by VMFS. Comparatively, Microsoft's Hyper-V does not currently offer a clustered file system, so each VM is provisioned a dedicated LUN. The forthcoming R2 release will make the .VHD files a clustered service (a new name for a clustered resource), with the clustered shared volume configuration for Microsoft Clustering Services.

The current problem is that the dedicated LUN-per-VM solution is too much to manage for most environments. The forthcoming clustered shared volume configuration will reduce the management aspect, but still be reliant on Microsoft Clustering Services.

Citrix takes a different approach with XenServer, which doesn't use clustered file systems. Although there is no clustered file system driver for XenServer, there is an API for native storage system benefits. So the Citrix strategy is to use a storage system benefit if you have it.

Both Hyper-V and XenServer accommodate large numbers of VMs on various storage systems, but the amount of work that an administrator has to do is less with VMFS. I like the approach from VMware best -- a virtual, platform-specific solution that serves as a gateway to the robust management features. Simply put, this just makes it easy for the administrator to manage the storage.